This application relates to and claims priority from Japanese Patent Application No. 2000-13934 filed on Jan. 18, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an air passage switching door for opening and closing an air passage through which air flows. More particularly, the present invention relates to a method for manufacturing the air passage switching door for a vehicle air conditioner.
2. Related Art
A conventional air passage switching system for a vehicle air conditioner has an air conditioning case for forming an air passage, and a butterfly door for switching the air passage. A rotation shaft for rotating the butterfly door is disposed at side end centers of the door. The butterfly door is rotatably held in the air conditioning case to be rotated by the rotation shaft. The butterfly door includes a door body portion made of resin having a high rigidity, and a lip-seal like seal member made of an elastomer.
When the door is manufactured, after the door body portion is inserted into a forming die, a melted elastic material is injected to a peripheral portion of the door body portion so that the seal member is formed integrally with the door body portion by an injection molding. Therefore, a shearing force is generated in an inner side of the elastic material due to the injection pressure during the injection molding of the seal member, and remains in the seal member as a shrinking force (inner stress).
Further, when the seal member (elastomer) is placed in a high-temperature condition after being injection-molded, the elastomer is heat-shrunken from this elastomer material characteristics. Accordingly, the seal member is readily deformed due to the inner shrinking force, and is readily bent upwardly at a corner portion.
In view of the foregoing problems, it is an object of the present invention to provide a method for manufacturing an air passage switching door where a thin and flat seal member made of an elastic material is attached to an outer peripheral portion of a door body. The manufacturing method can restricts a deformation of the seal member due to an inner shrinking force.
According to the present invention of the present invention, in a method for manufacturing an air passage switching door with a seal member continuously extending from an outer peripheral portion of a door body toward an outer side to have a thin plate-like shape, a melted elastic material is injected from plural injection gates provided at plural positions into a mold space within a forming die for forming the seal member of the door, and a flow length of the melted elastic material from each injection gate is equal to or smaller than 40 mm. Therefore, a flow resistance of the melted elastic material injected from the plural injection gates into the mold space can be made smaller, and a flow performance of the melted elastic material can be increased at a flow top end side. Thus, a cooling speed difference (i.e., temperature difference) or a pressure difference between each injection gate and the flow top end side can be reduced. Accordingly, even when the method is used for forming the air passage switching door where a length of one side seal member extending along the outer peripheral portion at one side of a rotation shaft is equal to or larger than 100 mm and a thickness of the seal member is equal to or smaller than 2.0 mm, a deformation of the seal member due to an inner shrinking force can be sufficiently restricted. As a result, a door sealing performance of the air passage switching door can be improved.
According to experiments by the inventors of the present invention, the method can be effectively used for forming the air passage switching door where the thickness of the seal member is equal to or smaller than 1.5 mm.
Preferably, in the injecting step, the flow length of the melted elastic material injected from each injection gate is set equal to or smaller than 30 mm. Therefore, a residual stress during a molding can be further reduced, and a corner deformation of the seal member can be further accurately restricted.
More preferably, the flow length of the melted elastic material injected from each injection gate is set to be in a range of 20-30 mm. Therefore, the air passage switching door can be manufactured in low cost, while the deformation of the seal member due to the inner shrinking force can be sufficiently restricted.